The effect of soil macroporosity, temperature and water content on CO2 efflux in the soils of different genesis and land management

This paper analyses the effects of soil macropores, temperature and water content on soil carbon dioxide (CO 2 ) efflux behaviour, which could help understand the mechanism of CO 2 efflux as influenced by soil type and land use methods.The temporal dynamic changes of CO 2 efflux from the soil surface using a closed chamber method (LI-COR LI-8100A Automated Soil CO 2 Flux System) were measured.Soil CO 2 efflux was investigated at a topsoil depth of 0-5 cm in (1) arable land under conventional tillage on Cambisol (CM), (2) grassland on Cambisol, (3) park on Cambisol, (4) arable land under conventional tillage on Retisol (RT), (5) grassland on Retisol and (6) forest on Retisol.CO 2 emission was measured six times per growing season from May to September in 2017.Soil macropore network was researched by implementing an X-ray computed tomography and carried out at the laboratory of the Institute of Agrophysics, Polish Academy of Sciences in Lublin, Poland.Macropores resulting from soil pedogenesis and land use methods played an important role on soil water, temperature and gas transport.The type of soil vegetation cover and amount of soil macropores significantly influenced soil respiration rate.The efflux values were recorded ranging from 0.71 to 3.43 μmol CO 2 m -2 s -1 (Cambisol) and from 0.70 to 3.05 μmol CO 2 m -2 s -1 (Retisol) in the grassland, from 0.43 to 2.57 μmol CO 2 m -2 s -1 (Cambisol) in the park, from 0.44 to 2.52 μmol CO 2 m -2 s -1 (Retisol) in the forest, from 0.52 to 2.68 μmol CO 2 m -2 s -1 (Retisol) and from 0.09 to1.57μmol CO 2 m -2 s -1 (Cambisol) in the conventional tillage.Computational tomography data revealed that the content of macropores amounted to 10.75% in the grassland site, 1.97% in the park and 1.21% in the conventional tillage within the soil depth of 3-8 cm of the Cambisol and 6.45% in the forest, 4.94% in the conventional tillage and 3.86% in the grassland at the same soil depth of the Retisol.Soil temperature, water content and macroporosity were the main factors exerting the influence on soil gas origination rate.The relationship between soil CO 2 efflux and volumetric water content at a 5 cm depth can be described by a linear regression model y = 0.0943x -0.7651, R 2 = 0.53 (valid for volumetric water content from 22.5 to 27.0 vol.% on Retisol and from 16.8 to 24.4 vol.% on Cambisol).Also, linear regression model y = 0.1167x -0.8214, R 2 = 0.65 showed the relationship between soil CO 2 efflux and soil macroporosity at the 3-8 cm depth.Soil CO 2 efflux displayed a typical polynomial relationship with soil temperature at the 5 cm depth; however, the relationship was very weak.Both soil type and land use methods had a noticeable influence on macroporosity, surface area and macropore range of soil pore-size distribution.The amount of macropores in macropore geometry was an important factor when dealing with CO 2 flow.Topsoil CO 2 efflux under contrasting vegetation cover and management conditions on Cambisol and Retisol was directly related to soil macroporosity and volumetric water content.